The court let stand the part of the law that requires law enforcement officers to check the immigration status of people they stop and suspect of being undocumented. Opponents of the law argued this provision would lead to racial profiling.

"The mandatory nature of the status checks does not interfere with the federal immigration scheme," Justice Anthony Kennedy wrote in his opinion. "Consultation between federal and state officials is an important feature of the immigration system. In fact, Congress has encouraged the sharing of information about possible immigration violations."

The court ruled, though, that three other parts of the law were an unconstitutional interference with federal law. Arizona may not make it a state crime for an undocumented immigrant to seek work, require immigrants to carry documentation and arrest someone based upon the suspicion that they are undocumented immigrants.

Kennedy was joined by Chief Justice John Roberts, a conservative, and three liberals -- Justices Ruth Bader Ginsburg, Stephen Breyer and Sonia Sotomayor. Conservative Justices Antonin Scalia, Samuel Alito and Clarence Thomas dissented in part, arguing the entire Arizona law should be upheld. Justice Elena Kagan, a liberal, recused herself from the case because she had worked on the case as President Obama's solicitor general.

President Obama announced earlier this month that the Justice Department would no longer deport undocumented workers who came to the United States as minors, had no criminal record, and had graduated from high school, obtained a G.E.D. or served in the military. Justice Scalia criticized Obama's decision in his dissent.

"The President said at a news conference that the new program is 'the right thing to do' in light of Congress's failure to pass the Administration's proposed revision of the Immigration Act. Perhaps it is, though Arizona may not think so. But to say, as the Court does, that Arizona contradicts federal law by enforcing applications of the Immigration Act that the President declines to enforce boggles the mind," Scalia wrote.

Jay Sekulow, Chief Counsel of the ACLJ, which filed an amicus brief with the Supreme Court representing 57 members of Congress and more than 65,000 Americans backing the Arizona law, praised the ruling.

"The Supreme Court took an important step forward in permitting states to protect their borders and citizens," he said. "While we're disappointed the high court failed to uphold all provisions of Arizona S.B. 1070, we're very pleased that the high court found this key provision constitutional, clearing the way for Arizona to continue its work to secure its borders and protect its citizens."

John W. Whitehead of The Rutherford Institute, which asked the court to declare the immigration law unconstitutional, said the ruling "does little to recognize or counteract the real danger inherent in S.B. 1070, which is the erection of a prototype police state in Arizona."

"By allowing Arizona police to stop and search people, citizens and immigrants alike, based only on their own subjective suspicions and visual observations, and by failing to address the core issue being debated here - namely, whether Americans have any Fourth Amendment protections anymore - the Court has opened the door to a host of abuses, the least of which will be racial profiling. Without fail, we will be revisiting this issue again."

Arizona's law has been copied by five other states -- Alabama, Georgia, South Carolina, Indiana and Utah. The part of the law requiring law enforcement to check the status of those suspected to be undocumented immigrants had been put on hold due to the lawsuits. It will now go into effect.

The Supreme Court did not rule Monday on the constitutionality of the Affordable Care Act (2010), or "Obamacare." That much anticipated ruling will be issued on Thursday at 10 a.m.